Conventional electrical machines in motor vehicles can be operated in generator mode or motor mode. Such electrical machines usually have a rotor having an exciter winding (rotor winding) through which an excitation current can flow, and a stator having a multi-phase stator winding to which a multi-phase phase voltage having a phase voltage vector can be applied.
Utilization of the electrical machine in a motor vehicle can require the electrical machine to be frequently switched on and off. It can prove to be problematic to switch on the electrical machine in particular at high rotation speeds. If the phase current is switched on first, large overshoots of the phase current can occur. If an excitation voltage is switched on first, a pole wheel voltage having a pole wheel voltage vector is initially induced in the stator; that voltage can interact negatively with the phase voltage that is to be switched on subsequently, which can cause large electrical and mechanical loads on the electrical machine.
German Patent Application No. DE 10 2013 215 306 A1 describes a method for switching on an electrical machine at high rotation speeds, the phase voltage being switched on exactly when it corresponds to the pole wheel voltage.